A major focus of our work involves an evaluation of the acute and chronic effects of ethanol in the CNS. However, the brain represents a heterogeneous collection of cell types, and distinction of direct and indirect effects of ethanol can be difficult. In vitro cell culture systems can be used to monitor specific, direct effects of ethanol, for comparison and contrast with results obtained in brain tissue and in vivo. Current studies of the effect of ethanol on NMDA receptors in primary cultures of cerebellar granule cells are now described in project AA00706. In addition, investigations of serotonin (5HT-3) receptors in NCB20 somatic cell hybrids are being performed, and are based on the findings that 1) ethanol enhances the action of agonists at the 5HT-3 receptor in electrophysiological studies of NCB20 cells, and 2) 5HT-3 receptor antagonists block the discriminative stimulus properties of ethanol (see Project AA00707). To determine whether ethanol directly affects the interaction of ligands with the 5HT-3 receptor, antagonist and agonist binding to these receptors were assessed by filter binding techniques. The antagonist, 3H-GR65630, bound to a single site on NCB20 membranes, and agonist (5HT, 2-Me-5HT) displacement curves were best fit by a one-site model. Ethanol (12.5 - 100 mM) had no significant effect on either agonist or antagonist binding, and may instead affect receptor-effector coupling processes. The behavioral studies suggest that the action of ethanol at the 5HT-3 receptor is important in mediating subjective effects of ethanol (e.g., reinforcement, intoxication) and studies in cultured cells may suggest a biochemical mechanism underlying these in vivo responses.